Control of stable posture and stance in humans and in animals is an active process involving central nervous system control. Posture control depends on the integration of sensory inputs, primarily somatosensory, visual and vestibular, and motor outputs. Responses of humans and animals to unexpected experimental perturbation of posture and stance by a moving platform are highly stereotyped in latency and configuration and involve specific muscle groups. The amplitude of the responses is context dependent and can be experimentally manipulated by creating conflicting sensory cues. This experimental program will develop an animal model for the study of mechanisms of central nervous system control of posture and stance, studies which cannot be performed in humans. The proposed experiments will utilize a moving platform coupled with a movable visual surround to study the dynamic control of posture and stance by the central nervous system of cats. The first objective is to quantitatively describe the features and organization of the automatic reflex responses to controlled platform perturbation including vertical and horizontal motion. The second objective is the investigation of the nature and location of the neural circuitry involved in the organization and generation of these responses as evoked by somatosensory cues. The last objective is the study of the involvement of somatosensory, visual and vestibular afferent information in the control of posture. This objective will include study of the contextual relationships of the three sensory inputs on posture control mechanisms in the resolution of conflicting sensory cues.